1. Field of the Invention
The present invention relates to a liquid crystal display device with a touch panel.
2. Description of the Related Art
A touch panel lapping over a display screen of an information communication terminal such as a computer, which has been used as an input device, has been widely used. Liquid crystal display devices that have been generally widespread as display devices are devices that change an orientation of a liquid crystal composition, which is sealed between two substrates of a thin film transistor substrate (hereinafter referred to as “TFT substrate”) and a color filter substrate, according to a change in electric field, and control a transmission degree of light that passes through the liquid crystal composition to display an image. Among those devices, in an IPS (in plane switching) system in which both of pixel electrodes and a common electrode are arranged on a TFT substrate side, a so-called lateral electric field is developed to realize a display having a wide viewing angle.
The touch panel is an input device that recognizes a position on a panel touched with a user's finger to allow a processing unit to conduct processing. As the touch panels, there have been known a resistance film type that detects a change in a resistance value of a touched portion, an optical sensor type that detects a change in the amount of light of a portion shielded by touch, and a capacitive coupling type that detects a change in capacitance. The capacitive coupling type has been widely used from the viewpoints that a transmittance of a panel is high, and a display image quality is not deteriorated, and that there is no contact with another electrode, and the durability is high.
FIG. 11 illustrates a touch panel 800 using the capacitive type. The touch panel 800 includes a glass substrate 806, drive electrodes 802 that are formed on the glass substrate 806, and extend in a lateral direction, detection electrodes 801 that extend in a longitudinal direction, and a touch panel control unit 808 that applies a voltage to the drive electrode 802, and detects a voltage or a current from the detection electrode 801. FIG. 12 illustrates a cross-section of FIG. 11 taken along a line XII-XII. As illustrated in the figure, the drive electrode 802 and the detection electrode 801 are formed in the same layer, and an insulating film 809 is formed on that layer. Also, a transparent shield electrode 807 for shielding an electric field developed from the display device is formed on a lower side of the glass substrate 806. Cross portions of the drive electrodes 802 and the detection electrodes 801 are formed so that the drive electrodes 802 and the detection electrodes 801 intersect with each other in different layers via through-holes so as not to contact with each other. In detection, a voltage of a pulse waveform is applied to the drive electrodes 802 in sequence, and a response of the detection electrodes 801 is sensed to detect whether the touch panel 800 has been touched, or not.
In recent years, upon a request for downsizing and thinning of the information communication terminal, a thinner liquid crystal display device with a touch panel has been demanded. JP 2009-244958 A discloses a thinner liquid crystal display device with a touch panel in which a common electrode of the liquid crystal display device is used as a drive electrode of the touch panel in the liquid crystal display device of an IPS type.